There are situations where it is desirable to have step attenuators for providing selected values of attenuation to an electrical circuit. Two basic forms of step attenuators have been used at radio and microwave frequencies. In one form a number of different attenuator pads are located on a rotating member and the desired attenuation is obtained by rotating the member to select the desired pad. In another form of step attenuator, a number of individual attenuators, of different values, for example progressing in binary order, such as 1 dB, 2 dB, 4 dB, and 8 dB, are connected in series. There is an individual switch pair for inserting or removal of each individual attenuator. By opening and closing the switches, it is possible to select any given value of attenuation up to the sum of the attenuations of all of the attenuators. Irrespective of the form of switching employed for selection of the individual attenuators, there is resistance in the switches. As a result, there is an error in the attenuation step created. The error arises by reason of the fact that the source and load impedances seen by the individual attenuators are mismatched to their characteristic impedance, due to the switch impedances.
The primary object of this invention is to achieve a high accuracy by overcoming the errors of the attenuation steps created by the aforesaid mismatch.
Furthermore, in practical application of attenuator cells, consisting of individual resistors, errors of the attenuation steps are observed due to reactive components of the resistors themselves and of their leads by which they are connected together to form said attenuator cells. Another object of this invention is to correct the attenuator for errors resulting from these reactances.